Transport Properties of the Infinite Dimensional Hubbard Model

Results for the optical conductivity and resistivity of the Hubbard model in infinite spatial dimensions are presented. At half filling we observe a gradual crossover from a normal Fermi-liquid with a Drude peak at $\omega=0$ in the optical conductivity to an insulator as a function of $U$ for temperatures above the antiferromagnetic phase transition. When doped, the ``insulator'' becomes a Fermi-liquid with a corresponding temperature dependence of the optical conductivity and resistivity. We find a $T^2$-coefficient in the low temperature resistivity which suggests that the carriers in the system acquire a considerable mass-enhancement due to the strong local correlations. At high temperatures, a crossover into a semi-metallic regime takes place.Comment: 14 page

Scanning tunneling microscopy and kinetic Monte Carlo investigation of Cesium superlattices on Ag(111)

Cesium adsorption structures on Ag(111) were characterized in a low-temperature scanning tunneling microscopy experiment. At low coverages, atomic resolution of individual Cs atoms is occasionally suppressed in regions of an otherwise hexagonally ordered adsorbate film on terraces. Close to step edges Cs atoms appear as elongated protrusions along the step edge direction. At higher coverages, Cs superstructures with atomically resolved hexagonal lattices are observed. Kinetic Monte Carlo simulations model the observed adsorbate structures on a qualitative level.Comment: 8 pages, 7 figure

Methods for estimating the case fatality ratio for a novel, emerging infectious disease.

During the course of an epidemic of a potentially fatal disease, it is important that the case fatality ratio be well estimated. The authors propose a novel method for doing so based on the Kaplan-Meier survival procedure, jointly considering two outcomes (death and recovery), and evaluate its performance by using data from the 2003 epidemic of severe acute respiratory syndrome in Hong Kong, People's Republic of China. They compare this estimate obtained at various points in the epidemic with the case fatality ratio eventually observed; with two commonly quoted, naïve estimates derived from cumulative incidence and mortality statistics at single time points; and with estimates in which a parametric mixture model is used. They demonstrate the importance of patient characteristics regarding outcome by analyzing subgroups defined by age at admission to the hospital

From ferromagnetism to spin-density wave: Magnetism in the two channel periodic Anderson model

The magnetic properties of the two-channel periodic Anderson model for uranium ions, comprised of a quadrupolar and a magnetic doublet are investigated through the crossover from the mixed-valent to the stable moment regime using dynamical mean field theory. In the mixed-valent regime ferromagnetism is found for low carrier concentration on a hyper-cubic lattice. The Kondo regime is governed by band magnetism with small effective moments and an ordering vector \q close to the perfect nesting vector. In the stable moment regime nearest neighbour anti-ferromagnetism dominates for less than half band filling and a spin density wave transition for larger than half filling. $T_m$ is governed by the renormalized RKKY energy scale \mu_{eff}^2 ^2 J^2\rho_0(\mu).Comment: 4 pages, RevTeX, 3 eps figure

Two-Channel Kondo Lattice: An Incoherent Metal

The two-channel Kondo lattice model is examined with a Quantum Monte Carlo simulation in the limit of infinite dimensions. We find non-fermi-liquid behavior at low temperatures including a finite low-temperature single-particle scattering rate, the lack of a fermi edge and Drude weight. However, the low-energy density of electronic states is finite. Thus, we identify this system as an incoherent metal. We discuss the relevance of our results for concentrated heavy fermion metals with non-Fermi-Liquid behavior.Comment: LaTex, 5 pages, 3 Postscript files. Revision - in reference 5 and 6(a

Application of a magnetic suspension balance to the oxidation study of the zirconium based alloys under high pressurewater vapour

International audienceThe fuel claddings in the Pressurised Water Reactor are corroded in water at high temperature and high pressure. The technical device ableto follow continuously the corrosion rate in conditions close to this medium does not yet exist. That is the reason why a high pressure thermogravimetric installation based on magnetic suspension has been designed to study in situ the oxidation kinetics of the zirconium based alloys under water vapour until 50 bars of pressure at 415°C. The accuracy of measurements is about 5•10–5 g under 2 bars, and 10–4 g under 50 bars. The reproducibility of measurements was verified and the deviation regarding post test weighing at room temperature is around 5•10–5 g what is clearly satisfying. Finally, the results presented in this work allow validating the high pressure thermogravimetric measurements obtained with this magnetic suspension device

Phase Diagram of the Two-Channel Kondo Lattice

The phase diagram of the two-channel Kondo lattice model is examined with a Quantum Monte Carlo simulation in the limit of infinite dimensions. Commensurate (and incommensurate) antiferromagnetic and superconducting states are found. The antiferromagnetic transition is very weak and continuous; whereas the superconducting transition is discontinuous to an odd-frequency channel-singlet and spin-singlet pairing state.Comment: 5 pages, LaTeX and 4 PS figures (see also cond-mat/9609146 and cond-mat/9605109

Multicanonical Hybrid Monte Carlo: Boosting Simulations of Compact QED

We demonstrate that substantial progress can be achieved in the study of the phase structure of 4-dimensional compact QED by a joint use of hybrid Monte Carlo and multicanonical algorithms, through an efficient parallel implementation. This is borne out by the observation of considerable speedup of tunnelling between the metastable states, close to the phase transition, on the Wilson line. We estimate that the creation of adequate samples (with order 100 flip-flops) becomes a matter of half a year's runtime at 2 Gflops sustained performance for lattices of size up to 24^4.Comment: 15 pages, 8 figure

The Hubbard Model at Infinite Dimensions: Thermodynamic and Transport Properties

We present results on thermodynamic quantities, resistivity and optical conductivity for the Hubbard model on a simple hypercubic lattice in infinite dimensions. Our results for the paramagnetic phase display the features expected from an intuitive analysis of the one-particle spectra and substantiate the similarity of the physics of the Hubbard model to those of heavy fermion systems. The calculations were performed using an approximate solution to the single-impurity Anderson model, which is the key quantity entering the solution of the Hubbard model in this limit. To establish the quality of this approximation we compare its results, together with those obtained from two other widely used methods, to essentially exact quantum Monte Carlo results.Comment: 29 pages, 16 figure